High definition television (HDTV) broadcast standards are defined by the Advanced Television Systems Committee (ATSC) of the “Digital HDTV Alliance” formed by U.S. television vendors. The ATSC A/53 Digital Television Standard states that equipment used for transmitting HDTV signals requires a timing accuracy of 10 ppm. Consumer electronic devices such as Digital Video Disc (DVD) players which will be used in conjunction with a digital television receiver therefore require a clock or timebase signal of similar accuracy, the clock signal typically being supplied by an internal stand alone reference oscillator. The cost and complexity of such an oscillator is a significant contributor to the total cost of the completed device.
Multivalue symbol vestigial sideband (VSB) modulation in accordance with the ATSC standard is a known modulation method for digitally transmitting information data such as HDTV signals. The recovery of data from the transmitted VSB signal containing digital video and related information at a digital receiver inherently requires the implementation of three functions: timing recovery for symbol synchronization, carrier recovery (frequency demodulation) and equalization. Timing recovery is the process by which the receiver clock (timebase) is synchronized to the transmitter clock by decoding the timing signal which is embedded in the transmitted VSB signal.
An example of a device to perform this function is disclosed in U.S. Pat. No. 5,943,369, entitled TIMING RECOVERY SYSTEM FOR A DIGITAL SIGNAL PROCESSOR, issued Aug. 24, 1999 to Knutson et al. A device for receiving quadrature amplitude modulated signals representing successive symbols is disclosed in U.S. Pat. No. 5,878,088, entitled DIGITAL VARIABLE SYMBOL TIMING RECOVERY SYSTEM FOR QAM, issued Mar. 2, 1999, issued to Knutson et al. The accuracy of the recovered timing signal is substantially equivalent to the accuracy of the transmitted VSB timing signal.